1. Field of the Invention
The invention relates to an apparatus for the continuous welding of abutting strips or sheets by means of a fixed laser beam, having disposed in pairs on both sides of the strips or sheets to be welded tension rollers extending perpendicularly to the direction of travel of the strips or sheets.
For the longitudinal seam welding of sheets or strips using a fixed welding device, the sheets or strips to be welded must be so guided that their edges abut one another, to allow problem-free welding. In the case of flexible sheets or strips it is difficult to bring their edges into abutment for welding without the sheets or strips overlapping one another, and to clamp them firmly abutted at least at the weld point.
2. Background Information
In U.S. Pat. No. 4,733,815, relating to the continuous welding of abutting strips, the welding device takes the form of a laser beam welding device and is disposed, viewed in the direction of travel of the strips, downstream of large-dimension tension rollers, in the zone of a group narrow guide rollers of substantially smaller diameter. In that device the welding head is disposed at a distance from the strips to be welded corresponding to the diameter of the guide rollers.
One difficulty in the continuous welding of abutting strips and sheets is the welding seam may develop irregularities and faults due to the fact that the strip or sheet edges abutting at the weld point arch in places and therefore do not lie flat one against the other. Such faults occur more particularly in the laser beam welding of thin strips and sheets with a small clamping surface, since due to arching the edges may move out of the zone of the laser beam weld spot--i.e., the zone of maximum energy transmission. The strips or sheets cannot be clamped close enough to the laser beam weld point by means of the aforementioned small-diameter guide rollers.